The invention relates generally to an image sensing (image pick-up) device and more particularly to the structure and mounting arrangement of solid state image sensing elements for reading images and the like and the structure or mounting arrangement of solid state image sensing devices having a plurality image sensing elements arranged in a line.
In general, image sensing devices include at least one transparent substrate chip having photoelectric converting elements formed thereon, cut from a transparent substrate having photoelectric converting elements formed thereon. However, conventional image sensing devices suffer from undesireably poor accuracy and reliability caused by problems associated with the mounting structure of the image sensing elements of these devices which cannot satisfactorily provide an elongated solid state image sensing device.
A first type of conventional image sensing device is described in Japanese Laid-open Patent Application No. 86363/84 which includes a large number of charge-coupled device (CCD) chips formed in a staggered arrangement on a single crystal silicon integrated-circuit (IC). The IC is electrically coupled to an external electrical circuit which performs complicated operations including delaying a signal in a manner so that the staggered arrangement has effects of a straight line arrangement.
A second type of conventional image sensing device is described in Japanese Laid-open Patent Application no. 126861/86, which includes a row of IC chips or the like in which the photoelectric converting elements located at the ends of the chip have a different form and structure than the other photoelectric converting elements on the chip.
A third type of conventional solid state image sensing device includes a transparent substrate typically formed of glass such as quartz glass or boro-silicate glass and has photoelectric converting elements formed thereon. Solid state image sensing devices of this type may be classified into the following two categories according to the manner at which light travels to the photoelectric converting elements:
(a) Arranged as shown in FIG. 12, in which a beam of light 803 enters an image sensing device 850 at a photoelectric converting element 802 disposed on the surface of a substrate 801; or
(b) An arrangement as shown in FIG. 13 in which a beam of light 901 enters an image sensing device 950 through a transparent substrate 801' and strikes a photoelectric converting element 802' disposed on the surface thereof.
The second arrangement (b) of device 950 is superior in the following respects. Arrangement (b) is not as severely dependent on the optical transparency of the upper exposed surface of photoelectric converting element 802 of device 850. Arrangement (a) requires the surface of element 802 to be sealed by glass having an extremely flat surface, whereas the protective coating or protective mold covering element 802' of device 950 may be selected from a wide variety of known coatings or molds and a highly reliable device can be produced. The structure of the photoelectric converting elements may also be selected from a wide variety of known structures and materials.
For these reasons, second arrangement (b) of device 950 is more frequently employed, and it is common to employ the arrangement of a sensing device 140 shown in FIG. 14. Sensing device 140 includes a transparent support 1001 having a transparent substrate chip 1004 secured thereon by a fixing agent 1002 and photoelectric converting elements formed on chip 1004. A circuit pattern 1010 is disposed on support 1001 and the photoelectric converting elements are electrically coupled to circuit pattern 1010 by a plurality of wires 1003 which can be formed of aluminum, gold, or the like. A mold material 1005 is disposed on and surrounds chip 1004. When device 140 is operating, incident light passes through transparent support 1001 and transparent substrate chip 1004 and strikes the photoelectric converting elements disposed thereon.
Sensing device 140 also includes a seal structure 1006 for preventing protective mold 1005 that covers the exposed surfaces of chip 1004 from flowing. The photoelectric converters and wires 1003 are disposed in protective mold 1005, which is typically formed of an organic polymeric material. Image sensing device 140 also includes a plurality of preamplifier circuits 1007, driver circuits or the like, which are formed on a printed circuit board and are electrically coupled by a connector 1008.
These Conventional mounting arrangements have drawbacks. The first type of arrangement, in which a plurality of chips supporting photoelectric elements are arranged in a line, is advantageous because it is convenient to position the chip connections associated with the in-line arrangement because the chips are disposed in a staggered manner. Further, it is not necessary to modify the structure of the photoelectric converting elements in the chip ends. However, this arrangement has more than two spaced rows of photoelectric converting segments and it is desireable to rearrange them into a single row.
To rearrange the segments into a single row, an additional external device is required to perform complicated electrical operations including delaying a signal. This additional device can be provided within the chips. In addition, because in this arrangement, the imaging segments are spaced in the secondary scanning direction, undesirable restrictions are places on additional necessary optical elements such as lenses. Further, this arrangement provides little degree of freedom in starting and stopping reading and thus its application to facsimile machines, for example, is limited. Thus, this arrangement is generally costly complicated and impractical to utilize.
The pitch between the photoelectric converting elements in the second type of conventional arrangement, in which a plurality of IC chips are disposed in a line, is made constant by forming or structuring the photoelectric converting elements differently at the ends of the chip than elsewhere on the chip. Accordingly, there is no continuity at the chip connection ends. To ensure the desired continuity, undesirable special electrical processes are required.
The third type of conventional arrangement has the following problems:
(1) Because light is introduced into the device through a transparent substrate having photoelectric converting elements formed thereon, the path of light passing through the device is complicated. It has been determined that irregular refraction and reflection is likely to occur and stray light can be reflected or refracted to the photoelectric converting elements and can degrade the resolution or gradient and limit reading speed.
To avoid this drawback, conventional devices such as a sensing device 150 having the cross-section shown in FIG. 15 can be provided in which s&gt;t * tan .THETA., wherein .THETA. is the maximum angle of incidence of light. Device 150 includes a transparent substrate 1101 having a transparent substrate chip 1102 of thickness "t" disposed thereon and a photoelectric converting element 1103 on chip 1102. Stray light such as an incident ray of light 1105 or 1106 from a side 1104 of chip 1102 cannot enter photoelectric converting element 1103. If "t" is 1 mm and .THETA.=15 , for example, than "s" is larger than 0.26 mm and an undesireably large useless region is present.
(2) Because transparent substrate chip 1102 is fixed on transparent support 1101, light must pass through transparent support 1101 and chip 1102 before striking element 1103. Therefore, support 1101 and the material fixing chip 1102 to support 1101 must be transparent, and these are various requirements imposed on their optical characteristics such as the refractive index. In addition, particularly in an in-line arrangement of transparent substrate chips, photoelectric converting elements are located close to the connections between chips. Thus, many requirements exist concerning the optical characteristics at the connection.
(3) The transparent substrate chips supporting the photoelectric converting elements and the transparent support are commonly formed of different materials. For example, the transparent substrate chips are commonly formed of highly heatresistant quartz. However, because the support has a wide surface area, it is commonly formed of an inexpensive glass, such as soda glass or boro-silicate glass. Thus, the coefficient of thermal expansion of the two materials commonly differ by about two orders of magnitude. Accordingly, separation or breakage is likely to occur therebetween, leading to low reliability.
FIG. 16 shows a device 1600 having a conventional arrangement of two substrate chips 1602 and 1603 fixed to a transparent substrate 1601 by a fixing agent 1605. The coefficient of thermal expansion of chips 1602 and 1603 secured greatly from that of substrate 1601. Accordingly, because the chips and substrate expand and contract by different amounts when device 1600 is heated and cooled, a plurality of gaps 1604 can form in fixing agent 1605, different portions of device 1600 will have different optical properties and the security of the bond of chips 1602 and 1603 to device 1600 is diminished. In view of these drawbacks, especially when considered together with the disadvantages noted in problem (2) it has been impractical to form image sensors with this arrangement.
(4) It is impractically difficult to properly mount the sensor device elements on the transparent support and driver circuits, preamplifier circuits and the like must be prepared separately.
(5) It is inconvenient to provide suitable structures for preventing the flow of the protective mold and additional manufacturing steps are required to add these structures.
Accordingly, it is desireable to provide an image sensing device which overcomes the disadvantages of the prior art.